fix(sky): keep the Sun and Moon, settle outside the ICRF tables

- Pass the custom sky box to the Viewer instead of `skyBox: false`, which
  also stopped CesiumWidget from creating the Sun and the Moon. Guarded by
  scripts/qa-sky-sun-moon.mjs.
- Outside the IAU 2006 tables (before 1975, after ~2050) the preload
  resolves without data; remember that span and stay on TEME instead of
  preloading and rendering every frame.
- The anime style no longer cel-shades the far plane, where four bands
  turned the faint Milky Way into blotches.
- Paint the planets out after the star-removing opening and with the
  ring median, so no brighter plateau is left; faces rebuilt.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

src/data/local_data/sky/README.md

@@ -42,10 +42,11 @@ Centre.
 (<https://www.eso.org/public/outreach/copyright/>). **Credit: ESO/S. Brunier.**
 
 **Changes made** (CC BY 4.0 asks for them to be stated): resampled to
-4096×2048, two planets (Jupiter, by position) painted over with the surrounding sky,
-stars removed with a 7×7 morphological opening, blurred (σ = 0.4°),
-reprojected from galactic coordinates to ICRF cube faces, black level set at
-the darkest 25 % of the sky, gamma-encoded and saved as WebP. Build:
+4096×2048, stars removed with a 7×7 morphological opening, two planets
+(Jupiter, by position) painted over with the median of the surrounding sky,
+blurred (σ = 0.4°), reprojected from galactic coordinates to ICRF cube faces,
+black level set at the darkest 25 % of the sky, gamma-encoded and saved as
+WebP. Build:
 `node scripts/build-milky-way.mjs <eso0932a.tif>`.
 
 The panorama is a photographic mosaic, not an astrometric map: bright stars